Intermittent motion device for high-speed rotating print drums

ABSTRACT

An intermittent, rotary motion mechanism which operates at the resonant frequency of its rotating system. The rotating system includes an input member, at least first and second output members (like first and second printer drums in a high-speed printer), and a resilient member (like a torsion shaft) interconnecting the first and second drums. An exciter (like a magnetic oscillator) is used to start the rotating system and keeping it oscillating at its resonant frequency to cause the first and second printer drums to dwell a predetermined number of times for each complete revolution of the input member as the input member is rotated at a constant velocity. The first printer drum experiences a dwell at a time when the second printer drum is rotating at substantially twice the velocity of the input member. More than two output members are utilized in other embodiments.

United States Patent Touchman [54] IN TERMITTENT MOTION DEVICE FOR HIGH-SPEED ROTATING PRINT DRUMS [72] Inventor: William S. Touchman, Kettering, Ohio {73] Assignee: The National Cash Register Company, Dayton, Ohio [22] Filed: Jan. 19, 1970 [21] Appl. No.: 3,690

[52] US. Cl. ..'...101/% c, 60/6, 310/93, 29/447 [51] Int. Cl ..B41j l/34, 1323p 11/02, E03b H00 [58] Field of Search ..101/93 C, 93 R, 93 MN, 96, 101/95; 29/447; 60/6; 310/103, 93; 318/47 [56] References Cited UNITED STATES PATENTS [151 3,654,859 [451 Apr. 11, 1972 3,505,950 4/1970 Harper ..101/93C 3,556,003 1/1971 Soderstrom ..l01/93C Primary Examiner-William B. Penn Attorney-Louis A. Kline, Albert L. Sessler, Jr. and Elmer Wargo [5 7] ABSTRACT An intermittent, rotary motion mechanism which operates at the resonant frequency of its rotating system. The rotating system includes an input member, at least first and second output members (like first and second printer drums in a highspeed printer), and a resilient member (like a torsion shaft) interconnecting the first and second drums. An exciter (like a magnetic oscillator) is used to start the rotating system and keeping it oscillating at its resonant frequency to cause the first and second printer drums to dwell a predetermined number of times for each complete revolution of the input member as the input member is rotated at a constant velocity. The first printer drum experiences a dwell at a time when the second printer drum is rotating at substantially twice the 3,216,348 1 1/1965 Oldenburg a1 101/93 C velocity of the input member. More than two output members 3,220,343 11/1965 Wasserman 101/93 C are utilized in other embodiments 3,309,988 3/1967 Touchman ..101/93 C 3,460,343 8/1969 Touchman ..60/6 21 Claims, 17 Drawing Figures 44 20 4s 2 48 5O 34 (PizllR ART) 38 52 45 3O 54 Essa: is 5s 24 V .1.

PATENTEDAPR 1 1 I972 SHEET 3 OF 5 wzv ms ATTORNEYS PATENTED PR 1 1 I912 13, 654, 859

SHEET 4 0F 5 FIG.?

NVENT WIL M S.TO MAN HIS ATTORNEYS PATENTEDAFR n 1912 3. 654,859 sum 5 or 5 A AAA HIS ATTORNEYS INTERMITTENT MOTION DEVICE FOR HIGH-SPEED ROTATING PRINT DRUMS BACKGROUND OF THE INVENTION No. 3,460,343, which issued on Aug. 12, 1969. These two :patents issued to applicant and are assigned to the assignee of the present application.

Themechanisms disclosed in said patents have only one outputmember, whereas the mechanisms of the present invention-employ two,-three, and more output members. The

use of at least two output membersin the present invention brings aboutthe following partial list of advantages:

'1. The size of the resilient means employed is reduced; for example, when a torsion bar is used as the resilient means, its length is about half the length of that employed in the mechanisms disclosed in said United States patents.

2. The exciter power (to excite the rotating system to resonance) is reduced by one half.

3. Theelimination of outboard reaction inertia members permits the use of physically smaller exciters.

4. The advantages brought about by items 1 through 3 above reduce the sound level of the resonant system by at least a factor of 2.

5. The procedure for exciting the rotating system to resonance is simplified.

6. Because at least two output members (like printer drums) are secured to one resilient means (like a torsion bar), the surfacearea for joining the drums to the torsion bar is doubled, thereby simplifying the joining thereof and making cemented joints feasible.

' 7. When this invention is used in a printer employing printer drums and print hammers, one half of the hammers are .fired 180 out of phase with the remaining half, thereby lowering the peak sound level of hammer firing.

8. Additional advantages will be mentioned during the detailed description of the invention.

SUMMARY OF THE INVENTION This invention relates to an intermittent rotary motion mechanism which operates at'the resonant frequency of its rotating system. The rotating system includes an input means, at leastfirst and second output means, and a resilient means interconnecting the input means with the first and second output means. An exciter means is used to start the rotating system and keep it oscillating at its resonant frequency to cause the first andsecond output means to periodically dwell a predetermined number of times for each complete revolution of the input means while the input means is rotated at aconstant velocity. The first output means experiences a dwell at a time when the second output means is rotating at substantially twice the velocity of the input means. Some of the embodiments of the invention utilize more than two output means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is an elevational view, similar to FIG. 2, third embodiment of the invention, drums as output members.

FIG. 5 is a front, elevational view of another embodiment of this invention, showing a device which operates on the principles of the embodiment shown in FIG. 2.

FIGS. 6A and 6B, taken together (FIG. 6B being on the sheet with FIGS. 9 and 10), show a cross-sectional view of the embodiment shown in FIG. 5 and are taken along the line 6- 6 in FIG. 5. FIGS. 6A and 6B show details of a hollow torsion shaft and means for removably mounting the output members of the embodiment, which members are printing drums.

FIG. 7 is a cross-sectional view taken along the line 7-7 of FIG. 6A, showing additional details of the means for removably mounting the printing drums.

FIG. 8 is a cross-sectional view taken along the line 8-8 of FIG. 6A, showing additional details of the means for removably mounting the printing drums.

FIG. 9, on the sheet with FIGS. 68 and 10, is a side view taken along the line 9-9 of FIG. 6B and shows details of a rotor of an exciter means used with the embodiment.

FIG. 10, on the sheet with FIGS. 68 and 9, is a side elevational view taken along the line 10-10 of FIG. 68, showing details of a stator used with the exciter means shown in FIG. 6B.

FIG. 11 is a front elevational view of another embodiment of the invention, having a removably mounted torsion shaft with printer drums attached thereto.

'FIG. 12 is an elevational view, similar to FIG. 9 but showing a portion of another embodiment of a rotor of an exciter which may be used with the device shown in FIGS. 6A and 6B. FIG. 13 is an elevational view taken along the line 13-13 of FIG. 12 and showing the profile of the poles or teeth of the rotor of the exciter of FIG. 12.

FIG. 14 is an elevational view, partly in cross-section, taken along the line 14-14 of FIG. 12 and showing additional details of the rotor.

FIG. 15 is an end view taken along the line 15-15 of FIG. 12 and showing additional details of the rotor.

FIG. 16 is a cross-sectional view of an enlarged portion of a stator means which is so constructed as to be compatible with the rotor shown in FIGS. 12 to 15 inclusive.

showing a having seven printing DESCRIPTION OF THE PREFERRED EMBODIMENTS Before proceeding with a description of the preferred embodiments, it seems appropriate to review some of the general principles of a basic intermittent motion device disclosed in said United States patents. I

The basic device 20 (FIG. 1) disclosed in said United States patents is incorporated within the framework 22 of a highspeed printer. The framework 22 has journal-type bearings 24, which receive the outer ends 26 and 28 of a torsion shaft 30, which is the resilient means in the device. An input of constant velocity rotation is supplied to the device by an input pulley 32, which is fixed to the shaft 30 at an enlarged-diameter portion 34 thereon. A driving belt 36, which is connected to a motor (not shown), is used to rotate the pulley 32.

The output member of the device 20 (FIG. 1) is a printing drum 38, which has printing characters 40 on its periphery. These characters 40 are aligned along the length of the drum along lines which are parallel to the rotating axes of the drum 38 and the torsion shaft 30. The drum 38 is fixed at its midpoint to the midpoint of the shaft 30 at an enlarged central portion 42 thereof.

The exciter means for the device 20 include stator and rotor means shown in FIG. 1. The stator means include stators 44 and 46, which are located in the framework 22, each stator having a coil 48 therein. The rotor means includes rotors 50 and 52, which are magnetically coupled to the stators 44 and 46, respectively. The rotors 50 and 52 are secured to enlarged cylindrical portions 54 and 56, respectively, of the shaft 30.

The operation of the basic device (FIG. 1) is disclosed in United States patents; however, a brief explanation thereof will follow. To start the device 20, the pulley 32 is rotated by a motor (not shown) until the shaft 30 and the drum 38 approach resonant speed, at which speed the coils 48 of the exciters are energized with a source of direct current to start the drum and the shaft oscillating and to keep them oscillating at the resonant frequency of the device. While oscillating at the resonant frequency, the drum 38 will periodically dwell a predetermined number of times for each complete revolution of the drive pulley 32. It is during the periodic dwells that print hammers, like 39, associated with the drum 38, are energized to effect printing on a paper inserted between the drum and the hammers. Because the printing is effected at a time when the drum 38 is experiencing a dwell, the printing is much clearer than that obtained by a printer having a drum which rotates at a constant velocity, as is done with the conventional on the fly" printers.

. FIG. 2 shows a first embodiment of the device of this invention, which is indicated generally as 58. The device 58 is incorporated into the framework 60 of a printer, as was done in FIG. 1. The framework 60 has therein journal or bushing-type bearings 62, which receive portions 64 and 66, respectively, of a torsion shaft 68, which is the resilient member in the device. The shaft 68 has a constant-diameter midsection, which tapers outwardly at areas 70 and 72 to form the enlarged-diameter portions 74 and 76, respectively. The areas 70 and 72 are reinforced areas which may be circular or elliptical in cross section, and the enlarged-diameter portions 74 and 76 are equidistantly spaced from the center 78 of the shaft 68, which also is a nodal point.

The output members of the device 58 are connected to its resilient member in the following manner. The output members include a first drum 80 and a second drum 82, as shown in FIG. 2. The drum 80 has an internal diameter 84, which is secured to the diameter portion 74 of the shaft 68 (the resilient member) by welding; for example, electron beam welding. The drum 80 has a constant wall thickness except for the reinforced area 86 (like a fillet), where the drum thickens near the internal diameter 84. The second drum 82 has an internal diameter 88 and also has a constant wall thickness extending along its length except for the reinforced area 90 (like a fillet) near the internal diameter 88, where the drum thickens. The drum 82 is secured to the shaft 68 by welding the internal diameter 88 of the drum to the diameter portion 76 of the shaft 68. The drums 80 and 82 have inner ends 92 and 94, respectively, which are slightly spaced from each other and the nodal point 78, so as to permit the drums to oscillate independently of each other. The shaft 68 has a reduced-diameter end portion 96, of predetermined flexibility, extending from the framework 60 and rotated by a motor 120 for supplying constant-velocity rotation to the device 58. The end portion 96 of the shaft 68 has a predetermined flexibility of such a value that it does not cause excitation at the resonant frequency of spring-mass systems external to the basic system including the shaft 68 and the drums 80 and 82. By this it is meant that the resonant frequency of the system including the shaft portion 96 and the rotor of the motor 120 should be low compared to the resonant frequency of the spring-mass system including the shaft 68 and the drums 80 and 82. The resonant frequency of this latter spring-mass system is, in effect, the forcing frequency of the external system including the shaft portion 96 and the rotor of the motor 120.

Each of the drums 80 and 82 (FIG. 2) has printing characters on its periphery. The characters are aligned parallel to the axis of rotation of the shaft 68 and the drums; however, the characters, like 98, of the drum 80 are offset slightly with respect to the characters, like 100, of the drum 82 when the device 58 is not in operation. When the device 58 is in operation, the characters 98 and 100, in effect, become aligned during a printing operation, so as to enable one continuous line of printing to be executed across the combined length of both drums and 82. This aspect will be discussed more fully during a description of the operation of the device.

The exciter means for the device 58 include stator and rotor means shown in FIG. 2. The stator means include stators 102 and 104, which are located in the framework 60, with each stator having an energizing coil 106 located therein. The rotor means include rotors 108 and 110, which are fixed to the shaft 68. The rotor 108 is magnetically coupled to the stator 102, and, similarly, the rotor 110 is magnetically coupled to the stator 104. The rotor 108 has poles or teeth 116 on its periphery, the number of teeth 116 being directly related to the number of dwells expected of the drum 80 for each complete revolution of the shaft 68, as disclosed in the above-mentioned United States patents, and, similarly, the stator 102 has thereon poles or teeth 118 corresponding to the number of teeth 116 on the associated rotor 108. If the number of characters to be printed by the drums 80 and 82 is 64, it follows that the number of teeth or poles on the stator 102 and the rotor 108 would be 64, and the drums 80 and 82 would dwell 64 times for each complete revolution of the input means. The rotor 110 and the stator 104 are identical to the rotor 108 and the stator 102, respectively; however, the exciter means on each end of the device 58 are phased I00 and 80 apart. For example, when the device 58 is in the idle state, the teeth or poles of the rotor and stator of the exciter means shown on the right of FIG. 2 are radially aligned, and the rotor teeth 116 of the exciter means shown on the left of FIG. 2 are positioned midway between the teeth 118 of the stator 102.

The device 58 (FIG. 2) operates in the following manner. A conventional electric motor 120, with slip torque" characteristics, is connected to the end 96 of the shaft 68 (having a predetermined flexibility, as previously explained) to rotate it at a constant velocity. As the shaft 68 is being accelerated up to operating speed, the coils 106 of both exciter means are energized with a direct current. Dynamically, the rotating system is driven at a nodal plane (passing through the point 78), and, when the coils 106 are energized, the exciter means at both ends of the shaft 68 cause forward and reverse pulses in the shaft, so that the drum 80 begins to oscillate opposed to the drum 82. These pulses build up torsional oscillations in the shaft 68 to the required steady-state amplitude, so that the drums 80 and 82, attached to its ends, oscillate opposed to each other at a definite peak-to-peak angle of oscillation. In essence, the motion of the drums (80, 82) is obtained by superimposing a cyclic torsional oscillation on a constantvelocity rotation. For each drum (80, 82), the torsional oscillations increase its rotational velocity during a positive half of the cycle and decrease its rotational velocity during the negative half of cycle. At the peak of its negative torsional oscillation, each drum is momentarily stationary relative to the framework 60. It is interesting to note that the periodic dwells for each drum (80, 82) occur when there is substantially no torsional stress in the shaft 68. Because the drum 80 is oscillating opposed to the drum 82, a dwell of one drum occurs exactly one half-cycle apart from the dwell of the other drum. If the forward rotation of the end portion 96 of the shaft 68 is clockwise (as viewed from the right-hand end of the device in FIG. 2), then the print hammers 122 associated with a group 124 of hammers (for the drum 82) would be conventionally actuated when the drum 82 reached a dwell position. As the end portion 96 of the shaft 68 continues its clockwise rotation, the drum 80 would reach a dwell one half-cycle later, and, accordingly, print hammers 126 associated with a group 128 of print hammers would be conventionally actuated to print in cooperation with the drum 80, leaving a print line having the same vertical registration as the print line from the drum 82. At least one of the drums 80 or 82 has its own conventional magnetic markings or other coding means and magnetic pickup (not shown) or other sensing means to provide for hammer actuation in correlation with drum position, so as to print a desired character in a particular print position, as is conventionally done. A line of characters 98 on the drum 80 is staggered with respect to a line of characters 100 on the drum 82 because the drums are oscillating opposed to each other and because the dwells of one drum occur one half-cycle apart from the dwells of the other drum.

The angle of oscillation of each of the drums 80 and 82 (FIG. 2) is controlled by the power input to the coils 106, which are DC-operated coils, and/or the voltage to the motor 120. Because the oscillatory velocity of the drums is a function of the angle of oscillation and the frequency (as disclosed in the above-mentioned United States patents), it is possible to achieve a controlled oscillatory velocity such that the instantaneous angular velocity of the drums (at print time) relative to the print hammers is zero. Because the angular velocity of drums approaching and leaving the zero point is asymptotic in character, there is a finite time, or dwell time, at equally spaced intervals when the motion of the drums 80 and 82 is sufficiently stationary relative to the associated print hammers to produce a high-quality print, a print which approaches letter-press quality.

In one embodiment of the device 58 (FIG. 2), the physical characteristics thereof are as follows. There are 64 character lines around the peripheries of the drums 80 and 82, each drum having a diameter of 3.250 inches, and the exciter means therefore having 64 teeth or poles to provide 64 dwells for each forward rotation of the drum. The constant forward rotation of the shaft 68 (at the node point 78) is 1,500 r. p. m., and the peak angle of oscillation of each drum 80 and 82 is approximately plus or minus 1. The effective dwell lasts for about 190 microseconds, with hammer actuation time of 90 microseconds within the effective dwell. The dwells occur at 1,600 cycles per second.

Some of the advantages of the device 58 (FIG. 2) over the device 20 shown in FIG. 1 are as follows:

1. The length of the torsion shaft 68 (FIG. 2) is approximately one half the length of the shaft 30 (FIG. 1), making removable drums and shaft feasible.

2. The power to the exciter means is reduced by approximately one half.

3. Elimination of outboard reaction inertias (like the enlarged portions 54 and 56 of FIG. 1) permits the use of smaller exciter means, making for a more compact device.

4. The above three advantages result in a substantial reduction in the noise level of the device 58.

5. Because half the hammers of group 128 (FIG. 2) are tired 180 out of phase with the hammers of group 124, the peak sound level of hammer firing is greatly reduced.

6. When two exciter means are used in the starting-up procedure of the device 58 of FIG. 2, they are arranged 180 out of phase with each other. Because they utilize less power than those shown in FIG. 1, their static torque is much less, making it unnecessary to wait until the motor 120 accelerates and almost reaches constant velocity rotation prior to energizing the exciter means. This facilitates the starting-up procedure.

7. In general, the construction shown in FIG. 2 is less expensive to manufacture than the one shown in FIG. 1.

FIG. 3 depicts a device which is another embodiment of this invention and which is designated generally as 130. The device includes a framework 132 having therein bearings 134 and 136, which receive reduced-diameter portions 138 and 140, respectively, of a torsion shaft 142, which is rotatably mounted therein. The shaft 142 has a reduced-diameter end portion 141, of predetermined flexibility (as previously defined), which is rotated at a constant velocity by a motor 144, similar to the motor 120. The device 130 has exciter means 146 and 148, which are identical to the exciter means shown on the left and right ends, respectively, of the device 58 of FIG. 2 with one exception, which will be noted later herein.

The device 130, depicted in a printer environment (FIG. 3), has three output members, which are secured to the torsion shaft 142 as follows. The output members of the device 130 are shown as printing drums having characters on their peripheries. The shaft 142 has, at its center, an enlarged diameter portion 150, which has reinforced areas, as previously described, to which portion a printing drum 152 is secured as follows. The drum 152 is thin-walled and tubular along its length and has a reinforced area 154 at its midpoint. The reinforced area 154 terminates in an internal diameter which is secured to the portion 150 on the shaft 142 by welding. The left-hand end of the shaft 142 also has a reinforced area 156, which terminates in an enlarged diameter which is secured to a reinforced area 158 of a second drum 160. The reinforced area 158 is secured to the area 156 by welding. A third printing drum 162, having a reinforced area 164 (identical to the area 156) is also welded to a reinforced area 166 (identical to the reinforced area 156) of the shaft 142. The masses of the drums 152, 160, and 162 are so designed that the mass of each drum and 162 is half the mass of the drum 152, the length of which is twice that of each of the drums 160 and 162. In effect, a spring-mass system represented by the drum 152 and portions of the shaft 142 is counterbalanced by a spring-mass system represented by the drums 160 and 162 and portions of the shaft 142. During operation, there are two nodal planes passing through the shaft 142 at 143 and 145; both of these nodal planes have the same forward rotation and velocity.

The device 130 (FIG. 3) operates in the following manner. The motor 144 is energized to rotate the end portion 141 of the shaft 142. As the shaft 142 is accelerated towards resonant frequency, the exciter means 146 and 148 are energized. These exciter means cause torque pulses on the shaft 142, which build up the oscillations of the drums 152, 160, and 162 to the desired, steady-state amplitude. In this embodiment, the drum 152 oscillates opposed to the drums 160 and 162; that is, when the drum 152 experiences a dwell, the drums 160 and 162 are each traveling at substantially twice the rotational velocity imparted to the end portion 141 of the shaft 142. A half-cycle later, both drums 160 and 162 experience a dwell, while the drum 152 is traveling at substantially twice the rotational velocity of the end 141. Because the drums 160 and 162 oscillate opposed to the drum 152, the exciter means 146 and 148 are constructed in phase with each other, whereas the exciter means shown on the left and right ends of the device 58 of FIG. 2 are 180 out of phase with each other. The phrase in phase as here used means that the rotor teeth or poles of both exciter means 146 and 148 are radially aligned with the respective teeth or poles of the associated stators when the device 130 is at a rest position.

When the device 130 (FIG. 3) is used in a high-speed printer environment, the characters on the drum and the print hammers are arranged in the following manner. Assuming a clockwise rotation of the end 141 of the shaft 142 (as viewed from the right-hand end of the device 130 in FIG. 3), the lines of characters (like 168) on the drum 152 are staggered with respect to the lines of characters (like 170) on the drum 160 and the lines of characters (like 172) on the drum 162. Print hammers 174, belonging to a first group 176, are conventionally actuated when a desired character in a particular print position is to be printed. The actuation of the print hammers 174 takes place during a time when the drum 152 is experiencing a dwell. Print hammers 178, belonging to a second group 180, are conventionally actuated when a desired character in a particular print position is to be printed. The actuation of the print hammers 178 takes place during a time when the drum 160 is experiencing a dwell, which is a half-cycle later than the drum 152. Print hammers 182, belonging to a third group 184, are conventionally actuated when a desired character in a particular print position (associated with the drum 162) is to be printed. The actuation of the print hammers 182 takes place during a time when the drum 152 is experiencing a dwell, which is simultaneously with the drum 160. As in the other embodiments, the actual printing takes place during the dwell of the associated drum, at which time the torsion shaft 142 has essentially no torsional stress therein. The individual drums 160, 152, and 162 have a clearance between adjacent ends to permit independent movement, as shown in FIG. 3.

FIG. 4 depicts a device which is another embodiment of this invention and which is designated generally as 186. The device includes a framework 188, having therein bearings 190 and 192 to receive reduced-diameter portions 194 and 196, respectively, of a torsion shaft 198, which is rotatably mounted therein. The shaft 198 has a reduced-diameter end portion 200, of a predetermined flexibility (as previously defined), which end portion is rotated at a constant velocity by a motor 202, similar to the motor 120. The device 186 has exciter means 204 and 206, which are identical to the exciter means 146 and 148, respectively, shown in FIG. 3.

The device 186, depicted in a printer environment (FIG. 4), has seven output members, which are secured to the torsion shaft 198. Because the device 186 is similar in construction and operation to the device 130, shown in FIG. 3, except for the number of output members, it will be described only generally herein. The output members include seven printer drums, 208, 210, 212, 214, 216, 218, and 220, which are secured to the torsion shaft 198, each drum being slightly spaced from the adjacent drum or drums to provide for independent movement thereof. Each of the drums is thin-walled for its length except for a reinforced area (like 222 on the drum 210), where the particular drum is joined to a reinforced area (like 224) on the torsion shaft 198. These reinforced areas are preferably elliptical or circular in cross section, as in the previously described embodiments.

The device 186 (FIG. 4) operates in the following manner. The motor 202 is energized to rotate the end 200 of the shaft 198. As the shaft 198 is accelerated towards resonant frequency, the exciter means 204 and 206 are energized. These exciter means cause torque pulses on the shaft 198, which build up the oscillations on the drums 208, 210, 212, 214, 216, 218, and 220 to the desired, steady-state amplitude. In this embodiment, the drum 214 oscillates opposed to the drums 212 and 216; the drum 210 oscillates opposed to the drum 212; the drum 208 oscillates opposed to the drum 210; the drum 218 oscillates opposed to the drum 216; and the drum 220 oscillates opposed to the drum 218. The drums 214, 210, and 218 may be considered as belonging to a first group of drums, while the drums 208, 212, 216, and 220 may be considered as belonging to a second group. When the drum 214 of the first group experiences a dwell, the drums 210 and 218 also simultaneously experience a dwell, and the drums 208, 212, 216, and 220 (of the second group) at this time are experiencing a velocity which is substantially twice the rotational velocity imparted by the shaft 200. A half-cycle later, the drums of group 2 experience a dwell, and the drums of group 1 experience a velocity which is substantially twice the rotational velocity imparted by the shaft 200. The characters on the drums of group 1 are aligned with one another along lines which are parallel to the longitudinal axis of the shaft 198, and, similarly, the characters of group 2 are aligned with one another along lines which are parallel to the same axis; however, the lines of characters of group 2 arestaggered with respect to the lines of characters of group 1 when both groups of drums are at rest, as shown. The exciter means 204 and 206 are in phase with each other, as previously described.

When the device 186 (FIG. 4) is used in a printer environment, printing is effected as follows. Each one of the drums of groups 1 and 2 enumerated above has its own group of print hammers associated with it. For example, the drum 208 has a group 226 of print hammers 228 associated with it, and, similarly, the drums 210, 212, 214, 216, 218, and 220 have associated therewith groups 210a, 212a, 214a, 216a, 218a, and 2200, respectively, of pring hammers 230. One print hammer is provided for each print position, and printing is effected when the associated drum is experiencing a dwell and the desired character to be printed is positioned at the print line, as explained in relation to the previous embodiments.

FIGS. 5, 6A, 6B, 7, 8, 9, and 10 show details of a device which is another embodiment of this invention and which is designated generally as 232. The device 232 operates on the same general principles disclosed in connection with the device 58, shown in FIG. 2; however, the device 232 features means for removably mounting the output members of the device, a hollow torsion shaft, and an improved oscillator means.

The general construction of the device 232 is best explained in conjunction with FIGS. 6A and. 6B. The device 232 is mounted in a left support means 234 and a right support means 236, which are secured to a base plate 238.

The right support means 236 (FIG. 63) includes a bracket 240, which envelops a cylindrical tubular member 242, which is adapted to be rotatably adjusted therein. The member 242 has an annular shoulder 244, which abuts against one side of the bracket 240 and is adjustably fixed therein by an annular plate 246 and fasteners 248. The internal diameter of the tubular member 242 is recessed at opposed ends to receive ball bearings 250 and 252, which are conventional angle contact bearings. The bearing 250 abuts against a shoulder 264 on a drive shaft 262. A sleeve 266 is positioned on the shaft 262 between the bearings 250 and 252, as shown. A lock washer 258 is positioned next to the bearing 252, and a nut 260, threaded on the shaft 262, is used to preload the bearings 250 and 252 and lock the drive shaft against axial movement in the right support means 236 while being driven. The shaft 262 is driven by a sleeve 266, which is fixed to the shaft by a pin 268, and the sleeve and the shaft are rotated by a driving belt 270, which is conventionally driven by a motor 272, similar to the motor (FIG. 2) and shown only diagrammatically in FIG. 6B.

The device 232 (FIGS. 6A and 6B) has first and second output members, which are driven by the shaft 262 in the following manner. In the embodiment shown, the first and second output members of the device 232 are tubular printer drums 274 and 276, respectively. The drum 274 is welded or cemented at one end to a sleeve 278, and, similarly, the drum 276 is welded or cemented at one end to a sleeve 280. The outermost ends at 282 and 284 of the sleeves 278 and 280, respectively (as viewed in FIGS. 6A and 6B), are reinforced, as previously explained, to distribute stresses. The end 282 is welded (as by electron beam welding) or cemented to one end 286 of a torsion shaft 288, which end 286 is also reinforced (as through the use of fillets), and, similarly, the end 284 is secured to the other end 290 of the torsion shaft 288. The torsion shaft 288 is tubular and is secured by cementing to a solid input shaft 292 at an area 294, which area is located at a nodal section (designated by the dashed line 296) of the torsion shaft 288.

The selection of the material of the torsion shaft is important, since it must have low hysteretic damping and be able to to continuously stand the high-frequency torsional stresses without failure. Considering quality, availability, and cost, the most successful material used to date for the torsion shaft 288 is vacuum melt 52-100 electric furnace steel. The entire shaft 288 is hardened and drawn to a hardness of approximately 58-62 Rockwell C, and the ends 286 and 290 are drawn back farther to a hardness of approximately 52-54 Rockwell C, the latter drawing operation being performed before and after electron beam welding.

As is apparent from the drawings, the input shaft 292 is located within the tubular torsion shaft 288. The input shaft 292 has conical recesses 298 and 300 in opposed ends thereof, as shown. The shouldered end of the driving shaft 262 is conical to complement the recess 300 and has a pin 302 passing therethrough, which pin also passes through suitable, diametrically opposed slots in the shaft 292 to form a driving connection to one end of the shaft 292. The other end of the shaft 292 is supported by a conical member 304, which is inserted in the recess 298 of the shaft 292. The conical member 304 is rotatably supported in the left support means 234, which will be described later herein. When the motor 272 is energized, it rotates both drums 274 and 276 in one direction by the driving connection just described.

The exciter means designated generally as 306 and 308 (FIGS. 6A, 6B, 9, and 10) perform the same function as the exciter means associated with the previously described embodiments; however, these exciter means are constructed somewhat difierently. Both exciter means 306 and 308 are identical; therefore a discussion of only one of them will follow.

The exciter means 308 (FIGS. 68, 9, and includes a rotor means (FIG. 9) and a stator means (FIG. 10). The rotor means includes a plurality of radially aligned teeth or poles 310, which are secured to an end wall 312 of the torsion shaft 288. The number of teeth 310 corresponds to the number of dwells of the drum 276 desired to each complete revolution of the input shaft 292. The stator means includes a first ring member 314 having therein an annular cavity into which a DC coil 316 is wound. A second ring member, 318, is secured to the first ring member 314 by screws and dowels (not shown) after the coil 316 is wound within said cavity. The first ring member 314 is secured to the face plate 256 by fasteners 320. The ring members 314 and 318 have thereon a plurality of aligned teeth 322 and 324, respectively, which are radially aligned, as are the teeth 310 on the rotor means. The number of teeth (FIG. 10) on the stator means corresponds to the number of teeth on the rotor means (FIG. 9), and, in one embodiment, the number was 64, which corresponds to 64 character positions around the periphery of the drums 274 and 276. The exciter means 306 and 308 are aligned 180 out of phase with each other, as already described in relation to FIG. 2. The cylindrical member 242 can be rotated within the bracket 240 (as previously described) to provide the means for making the phase adjustment. The clearance between the rotor and stator teeth is adjusted by placing a shim plate 254 between the ring member 314 and the face plate 256, as shown in FIG. 6B.

The characters on the drums 274 and 276 (FIG. 5) are arranged thereon in a manner similar to that shown in the device 58 of FIG. 2. The characters, like 326, are arranged in lines which are parallel to the rotating axis of the torsion shaft 288, and are staggered with respect to the lines of characters, like 328 on the drum 274, when the device 232 is inoperative and both drums are stationary. When the device 232 is in operation, each drum 274 and 276 becomes aligned with an associated group of print hammers (shown as dashed lines 330 and 332, respectively, in FIGS. 6A and 68) when the particular drum experiences a dwell during operation at the resonant frequency, as previously explained in connection with the device 58 (FIG. 2). At least one of the drums 274 or 276 has its own conventional magnetic markings or other coding means and magnetic pick-up or other sensing means (not shown), which are conventionally used to effect a printing of a particular character at a particular print position by energizing the associated print hammer in the groups 330 and 332, as was done with the device 58 of FIG. 2.

The left support means 234 (FIGS. 5, 6A, 7, and 8), previously mentioned, enables the drums 274 and 276 and the shafts 288 and 292 to be removed as a unit from the base plate 238 by the following construction. The conical member 304, which supports the input shaft 292, is rotatably supported in bearings 334 and 336, which are spaced apart by concentric spacers 338 and 340. The bearings 334 and 336 are supported in a cavity 342, located in one end of a generally cylindrical member 344. The bearing 334 abuts against an annular shoulder 346, located in the cavity 342, and the bearing 336 abuts against an annular shoulder 348 on the conical member 304. A washer and C-shaped fastener 350 are used to secure the bearings 334 and 336 to the conical member 304. The member 344 has a face plate 352, to which the stator means of the exciter means 306 is secured.

The generally cylindrical member 344 is movably mounted on a base 354 for movement in an axial direction relative to the longitudinal axis of the input shaft 292 by the following construction, shown in FIG. 6A, 7, and 8. The member 344 has a first pair of diametrically opposed grooves, 356 and 358, in its outer wall, and a second pair of diametrically opposed grooves, 360 and 362, also in its outer wall, as shown. The base 354 has blocks 364 and 366 secured thereto, which blocks have grooves 368 and 370, which are aligned with the grooves 356 and 358, respectively. A ball bearing 372 is positioned between the grooves 356 and 368, and a ball bearing 374 is positioned between the grooves 358 and 370 to support the right-hand end (as viewed in FIG. 6A) of the member 344 for the axial movement mentioned. Suitable pins, like 376 in the blocks 364 and 366, and pins 378 in the member 344 are used to retain the bearings 372 and 374 in their associated grooves. The left-hand end (as viewed in FIG. 6A) of the member 344 is supported by blocks 380 and 382, grooves 384 and 386, the grooves 360 and 362, bearings 388 and 390, and pins 391, which are analogous to their counterparts on the right-hand end of the member 344, already described.

The lever means for moving the generally cylindrical member 344 in an axial direction relative to the longitudinal axis of the input shaft 292 is shown in FIGS. 6A, 7, and 8 and is constructed in the following manner. The lever means includes a bell crank lever 392, which is located in a slot 394 in the member 344. The lever 392 is pivotally mounted on a pin 396 passing through the member 344; it has an operating handle 398 mounted on one arm thereof, and its other arm is pivotally joined to one end of a link 400 by a pin 402. The remaining end of the link 400 is pivotally joined to a plunger 404 by a pin 40 6. The plunger 404 is reciprocatingly movable in a bore 408 located in a block 410, which is secured to the base 354. The plunger 404 is spring-urged to force the member 344 to the right (as viewed in FIGS. 6A and 7) by a spring 412 located in the bore 408, when the lever 392 is in the above-dead-center position, shown in FIG. 7. Movement of the member 344 to the right enables the conical member 304 to engage the recess 298 on the input shaft 292, thereby rotatably supporting the adjacent end of the shaft. A C-shaped washer 414, inserted in an appropriate annular recess on the shaft 416, associated with the plunger 404, limits the movement of the plunger 404 to the right (as viewed in FIG. 7).

To remove the drums 274 and 276 and the shafts 288 and 292 from the supporting conical member 304 and the drive shaft 262, the following procedure is used. The operating handle 398 is moved to the left, as viewed in FIGS. 5, 6A, and 7. Moving the handle to the left causes the link 400 to rotate clockwise (as viewed in FIG. 7) about the pin 406, and the lever 392 to rotate counterclockwise about the pin 396. Continued rotation of the lever 392 in this direction causes the pin 396 to be moved to the left, pulling the cylindrical member 344 to the left along the conical member 304. The end of the lever 400 near the pin 402 drops into a well 403 provided for this purpose. The drums 274 and 276 may be temporarily rested on felt-lined cradles 418 (which are secured to the base plate 238) prior to removal of the drums. Because the drums can be removed easily, a different set of drums, having a different style of printing, or front, can be easily installed.

To install the drums 274 and 276 (FIGS. 6A and 6B), the following procedure is used. The diametrically opposed slots in the right-hand end of the shaft 292 (as viewed in FIG. 6B) are aligned with the pin 302 in the driving shaft 262. The lefthand end of the shaft 292 is then aligned with the conical member 304 as the operating handle is moved to the right to advance the member 304 into the recess 298 on the shaft 292. Some adjustment is provided by making the base 354 adjustable on the base plate 238; conventional T-shaped clamps 419 (FIG. 8) may be used for this purpose.

Because the shaft 292 experiences only constant velocity rotation, ball bearings like 250, 252, 334, and 336 (FIGS. 6A and 68) may be used in the network supporting it. Bearings 420 and 422, shown in FIGS. 6A and 6B, respectively, must withstand the torsional oscillation of the torsion shaft 288 relative to the steady-rotation shaft 292. Since there is no forward rotation of the torsion shaft 288 relative to the shaft 292, the use of porous bronze for the bearings 420 and 422 has been somewhat unsatisfactory, since a hydrodynamic oil film cannot be maintained. Since the device 232 operates quite well with the bearings 420 and 422 removed, the approach taken was to make the bearings 420 and 422 of a good dry friction material, with extra clearance between said bearings and the shaft 292. The bearings 420 and 422 then serve only as snubbing devices in case the combined mass of the torsion shaft 288 and the drums 274 and 276 is set into oscillation by the action of the pring hammers against said print drums.

Some of the advantages of the device 232 (FIGS. 6A and 68) over that already mentioned in relation to the device 58 (FIG. 2) are as follows. Because the shaft 288 is hollow, the quality of the shaft is higher, due to advantages gained in the heat treatment thereof. Also, should the shaft 288 fail, the drums 274 and 276 would still be supported on the shaft 292,

thereby preventing damage to the characters on the drums or to the drums themselves. The exciter means 306 and 308 provide a more stable radial equilibrium than the ones shown in the device 58 of FIG. 2.

FIG. 11 shows another embodiment of the device of this invention, which is indicated generally as 424 and is constructed as follows. The device 424 includes a framework 426, having semi-circular supporting members 428 and 430 onits ends. A cylindrical mounting member 432 is positioned in the supporting member 430 and is detachably secured therein by a conventional clamping device 434. A similar cylindrical mounting member 436 is positioned in the supporting member 428 and is detachably secured therein by a clamping device (not shown)identical to the device 434.

The device 424, shown in FIG. 11, is utilized in a high-speed printer environment, and, consequently, its output members are printer drums 438 and 440. The printer drum 438 is tubular and has a reinforcing sleeve 442 secured to its inside, as shown. The device 424 includes a torsion shaft 444, which has a mounting cone 446, whose outer periphery is secured to the sleeve 442 at its midpoint. The shaft 444 also has a reduceddiameter portion 448, to which a rotor member 450 is secured to rotate therewith. The shaft 444 also has another reduceddiameter portion 452, of a predetermined flexibility, which extends between the portion 448 and an enlarged-diameter portion 454. A cylindrical member 456 is secured to the portion 454 to rotate therewith, and the member 456 has a tubular sleeve 458 extending from one side thereof so as to surround some of the reduced-diameter portion 452. The sleeve 458 is rotatably supported within the cylindrical mounting member 436 by ball bearings 460 and 462. A stator member 464, having a DC coil 466 located therein, is secured to the cylindrical mounting member 436. The rotor member 450 and the stator member 464 constitute an exciter means designated generally as 468, which exciter means is similar to that utilized in FIGS. 9 and 10. Because the member 436 can be adjustably rotated and fixed to the supporting member 428, a phasing of the stator member 464 of the exciter means 468 relative to the exciter means 470 can be done as previously explained. The

right-hand side of the device 424 is identical to its left side, which has already been described except for one area. The cylindrical member 472 has a driving dog 474 extending from its outer face and fitting into a complementary recess on a driving member 476, which supplies the constant rotary motion to the device 424. The drum 440 has a group of characters 478, which are arranged in lines which are staggered with respect to the lines of characters 480 on the drum 438 for the purpose previously described. Printing is effected as previously described.

Some special points of interest relating to the device 424 (FIG. 1 l) are as follows. The fundamental resonant frequency of a first system of the device 424 is determined by the inertial mass of the print drum 438, the sleeve 442, and a mounting cone 446 on each end of the torsion shaft 444. The reduceddiameter portion 452 of the torsion shaft 444, the enlargeddiameter portion 454, and the cylindrical member 456 are included in a second system, which also has a resonant frequency. However, if the resonant frequency of the second system, including the reduced-diameter portion 452, is considerably lower than the first system, including the printer drum 438, the amplitude of the torsional oscillations of the cylindrical member 456 relative to the nodal section N-N (shown as a dashed line) will be so small as to approach zero. The cylindrical member 456, under these conditions, will experience substantially only continuous rotary motion, making the use of the ball bearings 460 and 462 feasible. The construction of the right-hand end of the device 424, as viewed in FIG. 11, is identical to the left-hand end of the device, shown in cross section and already described.

It is interesting to note that, even though the device 424 is mounted on conventional ballv bearings, the system has no points of dry friction, as explained in the case for the device 232 (the bearings 420 and 422, shown in FIGS. 6A and 6B). In other words, the mechanical Q of the system can be made very high as a result of the interface damping approaching zero.

FIGS. 12 to 16 inclusive show a portion of another embodiment (designated generally as 482) of a rotor means of an exciter means which may be used, for example, in the embodiment 232, shown principally in FIGS. 6A and 6B. The sides of the teeth 310 shown in the rotor means of FIG. 9 and the stator meansof FIG. 10 are perpendicular to their faces, so as to present, in profile, a square tooth design. The profiles of the teeth or poles of the rotor means in the embodiment 482 are generally trapezoidal, as will be explained hereinafter.

The profile of the teeth or poles of the'rotor means of the embodiment 482 is shown principally in FIGS. 13 and 15. Each tooth or pole 484 has a face 486 with adjoining sides 488 and 490. The teeth 484 are so designed that the included angle between two adjacent teeth'(as measured by the angle A in FIG. 13) is about 70. The ratio of the distance between adjacent teeth 484 (as measured by y in FIG. 13) relative to the width of the face 486 of a tooth (as measured by x) is approximately four. In the embodiment shown, the distance between adjacent teeth 484 at their bases (as measured at d) is approximately 0.030 inch. This distance d is maintained between the teeth from their outer perimeter, shown in FIG. 13, to their inner perimeter, shown in FIG. 15. To form the teeth 484, a single rotary cutter (not shown) is used. The path of the cutter relative to the faces 486 of the teeth is such that the base of the teeth (as shown by the line 492 in FIG. 14) makes an angle of about 3 (as measured by the angle B in FIG. 14) with a plane including the faces 486 of the teeth 484. This plane including the faces 486 is perpendicular to the rotating axis of the rotor means. The cutter moves along radial lines to form the radially aligned teeth 484, whose faces 486 are best shown in FIG. 12. Because the teeth 484 are radially aligned, the width (x) of each tooth face and the distance (y) between adjacent teeth become less as these distances are measured closer to the rotating axis of the exciter means; however, the ratio between these distances remains approximately four, as previously explained.

A portion of a stator means to be used with the rotor means shown in FIGS. 12 to 15 inclusive is shown in FIG. 16. The stator means generally designated as 494 in FIG. 16 is similar to the stator means of the exciter means 308 shown in FIG. 68 except for a change in tooth design and means for coil insertion and removal. The teeth 496 of the stator means 494 match the profile of the teeth 484 of the rotor means shown principally in FIGS. 13 and 15, and are formed by the general method previously explained. The stator means 494 includes a first ring member 498 and a second ring member 500 having an annularly-shaped DC-operated coil 502 positioned therebetween as shown. The first ring member 498 has a surface 504, which is mounted to the face plate 256 (FIG. 63) when used therein. The teeth 484 of the rotor are interrupted as at 506 (FIG. 14) to match the interruption of the teeth 496 as at 508 (FIG. 16).

The chief advantages of the exciter means of FIGS. 12 to 16 inclusive over the one shown in FIGS. 9 and 10 are that:

a. The dwell characteristics of the rotating drums of the device 232 of FIGS. 6A and 6B are sharpened when using a tooth profile as shown in FIGS. 12 to 16 inclusive.

b. The teeth shown in FIGS. 12 to 16 inclusive cause less axial pull in the bearings supporfing the rotating drums and shafts of FIGS. 6A and 68 than do the teeth shown in FIGS. 9 and 10.

c. The exciter means shown in FIGS. 12 to 16 inclusive reduce the noise level of the device 232 of FIGS. 6A and 68.

d. The teeth shown in FIGS. 12 to 16 inclusive can be manufactured more readily and economically than the ones shown in FIGS. 9 and 10.

I claim:

1. A printer comprising rotatable input means including a torsion shaft having first and second connection areas thereon;

rotating means for rotating said input means at a substantially constant velocity;

first and second printer drums secured to said first and second connection areas respectively, said drums having printing characters thereon; and

magnetically operated exciter means including a first exciter located near one end of said torsion shaft and a second exciter located near the remaining end thereof; said exciters being adjusted to operate 180 out of phase with each other; each said exciter acting on its associated end of the torsion shaft to retard its rotation as the torsion shaft is rotated by said rotating means to cause said drums to oscillate in opposed relationship to each other at substantially the resonant frequency of said input means and drums to produce a dwell in the rotational movement of each drum for a cycle of oscillation, with the first printer drum experiencing any one of said dwells at a time when the second printer drum is rotating at substantially twice the velocity of said input means;

said rotating means including an input shaft of predetermined flexibility being connected to one end of said torsion shaft to rotate it.

2. A printer comprising rotatable input means including a torsion shaft having first,

second, and third connection areas thereon;

rotating means including an input shaft of predetermined flexibility being connected to one end of said torsion shaft to rotate said input means at a substantially constant velocity;

first, second, and third printer drums secured to said first, second, and third connection areas respectively; said drums having printing characters thereon; and

magnetically operated exciter means acting on the opposed ends of said torsion shaft to retard them as the torsion shaft is rotated by said rotating means to cause the second drum to oscillate in opposed relationship with said first and third drums at substantially the resonant frequency of said drums and input means to produce a dwell in the rotational movement of each said drum for a cycle of oscillation, with the second drum experiencing any one of said dwells at a time when the first and third drums are rotating at substantially twice the velocity of said input means.

3. A printer comprising:

a rotatable input means including a tubular torsion shaft having first, second, and third connection areas thereon; rotating means for rotating said input means at a substantially constant velocity and including an input shaft means which includes an input shaft inserted inside said torsion shaft and is secured to said third connection area, which is located inside said tubular shaft;

first and second printer drums secured to said first and second connection areas respectively, said drums having printing characters thereon; and

magnetically operated exciter means including a first exciter located near one end of said torsion shaft and a second exciter located near the remaining end thereof; said exciters being adjusted to operate 180 out of phase with each other; each said exciter acting on its associated end of the torsion shaft to retard its rotation as the torsion shaft is rotated by said rotating means to cause said drums to oscillate in opposed relationship to each other to produce a dwell in the rotational movement of each drum for a cycle of oscillation, with the first of said printer drums experiencing any one of said dwells at a time when the second printer drum is rotating at substantially twice the velocity of said input means.

4. The printer as claimed in claim 1 in which the characters on said first and second drums are arranged in lines with the lines of characters of said first drum being staggered with respect to the characters on the second drum when the drums are at rest, but the lines of characters of both said drums become aligned with a printing line during the dwells of their respective drums when oscillating at said resonant frequency; said lines of characters being parallel to one another and to the rotating axis of said shaft.

5. The printer as claimed in claim 1 in which said first and second drums have equal rotating masses, and each of said drums has an inner end and an outer end, with the first drum having its outer end secured to said first area and the second drum having its outer end secured to said second area; the inner ends of said drums being adjacent to and spaced from each other.

6. The printer as claimed in claim 2 in which said third connection area on said torsion shaft is midway between said first and second connection areas and in which said drums have rotating axes which are coincident with the rotating axis of said shaft.

7. The printer as claimed in claim 2 further comprising first, second, and third groups of print hammers positioned along a print line and associated with said first, second, and third printer drums, respectively;

each of the hammers of said groups of hammers being adapted to be energized when the associated one of said drums is experiencing a dwell.

8. The printer as claimed in claim 7 in which the characters on said first, second, and third drums are arranged in lines which are parallel to the said rotating axis of said shaft; said lines of characters on said first and second drums being aligned with each other but offset with respect to the lines of characters on said third drum.

9. The printer as claimed in claim 13 further comprising first and second groups of print hammers positioned along said print line and associated with said first and second printer drums, respectively;

each of the print hammers of said groups of hammers being adapted to be energized when the associated one of said drums is experiencing a dwell.

10. The printer as claimed in claim 3 in which said rotating means further comprises:

a driving shaft detachably connected to one end of said input shaft; and

support means for detachably and rotatably supporting the remaining end of said input shaft so as to enable said input shaft along with said torsion shaft, and said first drum and second drum secured thereto to be removed as a unit from said printer.

11. The printer as claimed in claim 2 in which said first and second exciters are adjusted to operate in phase with each other.

12. The printer as claimed in claim 11 in which the second drum has a rotating mass which is equal to the combined rotating mass of said first and third drums.

13. The printer as claimed in claim 3 in which the characters on said drums are arranged in lines, with the lines of characters on the first printer drum being staggered with respect to the lines on the second drum when the drums are at rest; but the lines of characters of both of said drums become aligned with a printing line during the dwells of their respective drums.

14. The printer as claimed in claim 3 in which each said exciter has radially aligned stator poles and rotor poles lying in planes which are parallel to and spaced from each other and which planes are perpendicular to the rotating axes of said first and second drums; said poles being trapezoidally shaped in cross section, with the rotor poles being attached to the torsion shaft for rotation therewith and the stator poles being stationary relative thereto.

15. A printer comprising:

rotatable input means including a torsion shaft having a plurality of connection areas thereon;

rotating means for rotating said input means at a substantially constant velocity;

first and second groups of printer drums, with each said drum being secured to said torsion shaft at one of said connection areas; and

magnetically operated exciter means acting on the opposed ends of said torsion shaft to retard them as the torsion shaft is rotated by said rotating means to oscillate said first and second groups of drums at substantially the resonant frequency of said input means and drums to cause each group of drums to periodically dwell a predetermined number of times for each revolution of said input means; the drums of the first group experiencing said dwells at times when the drums of the second group are rotating at substantially twice the velocity of said rotating means;

said exciter means including a first exciter located near one of said opposed ends of said torsion shaft and a second exciter located near the remaining said end; and

said rotating means including a shaft of predetermined flexibility being connected to one end of said torsion shaft.

16. The printer as claimed in claim 15 further comprising first and second groups of print hammers associated with the first and second groups of drums respectively; the first and second groups of print hammers being selectively actuated to effect printing when the drums of their associated groups are experiencing one of said dwells.

17. The printer as claimed in claim 16 in which said drums have lines of characters thereon, with the lines being parallel to the rotating axis of said drums; and with the lines of characters of the drums of the first group being staggered with respect to the lines of characters of the drums of the second group.

18. The printer as claimed in claim 1 in which said rotating means further includes an extension shaft on the remaining end of the torsion shaft, which extension shaft is identical to said input shaft;

reaction masses secured to the free ends of said input and extension shafts;

each said reaction mass having a supporting member to rotatably support the torsion shaft; and

means for rotating the reaction mass secured to the input shaft at a constant velocity.

19. The printer as claimed in claim 18 in which each supporting member is a tubular extension of its associated reaction mass, with each said tubular extension extending towards the associated said first and second connection areas and providing a bearing surface for rotatably supporting the torsion shaft.

20. The printer as claimed in claim 19 in which the characters on said drums are arranged in lines, with the lines of characters of the first drum being staggered with respect to the lines of characters of the second drum while the drums are at rest, but the lines of characters of both said drums become aligned with a printing line during the dwells of their respective drums.

21. The printer as claimed in claim 20 in which each said exciter has radially aligned stator poles and rotor poles lying in planes which are parallel to each other and perpendicular to the rotating axis of the torsion shaft. 

1. A printer comprising rotatable input means including a torsion shaft having first and second connection areas thereon; rotating means for rotating said input means at a substantially constant velocity; first and second printer drums secured to said first and second connection areas respectively, said drums having printing characters thereon; and magnetically operated exciter means including a first exciter located near one end of said torsion shaft and a second exciter located near the remaining end thereof; said exciters being adjusted to operate 180* out of phase with each other; each said exciter acting on its associated end of the torsion shaft to retard its rotation as the torsion shaft is rotated by said rotating means to cause said drums to oscillate in opposed relationship to each other at substantially the resonant frequency of said input means and drums to produce a dwell in the rotational movement of each drum for a cycle of oscillation, with the first printer drum experiencing any one of said dwells at a time when the second printer drum is rotating at substantially twice the velocity of said input means; said rotating means including an input shaft of predetermined flexibility being connected to one end of said torsion shaft to rotate it.
 2. A printer comprising rotatable input means including a torsion shaft having first, second, and third connection areas thereon; rotating means including an input shaft of predetermined flexibility being connected to one end of said torsion shaft to rotate said input means at a substantially constant velocity; first, second, and third printer drums secured to said first, second, and third connection areas respectively; said drums having printing characters thereon; and magnetically operated exciter means acting on the opposed ends of said torsion shaft to retard them as the torsion shaft is rotated by said rotating means to cause the second drum to oscillate in opposed relationship with said first and third drums at substantially the resonant frequency of said drums and input means to produce a dwell in the rotational movement of each said drum for a cycle of oscillation, with the second drum experiencing any one of said dwells at a time when the first and third drums are rotating at substantially twice the velocity of said input means.
 3. A printer comprising: a rotatable input means including a tubular torsion shaft having first, second, and third connection areas thereon; rotating means for rotating said input means at a substantially constant velocity and including an input shaft means which includes an input shaft inserted inside said torsion shaft and is secured to said third connection area, which is located inside said tubular shaft; first and second printer drums secured to said first and second connection areas respectively, said drums having printing characters thereon; and magnetically operated exciter means including a first exciter located near one end of said torsion shaft and a second exciter located near the remaining end thereof; said exciters being adjusted to operate 180* out of phase with each other; each said exciter acting on its associated end of the torsion shaft to retard its rotation as the torsion shaft is rotated by said rotating means to cause said drums to oscillate in opposed relationship to each other to produce a dwell in the rotational movement of each drum for a cycle of oscillation, with the first of said printer drums experiencing any one of said dwells at a time when the second printer drum is rotating at substantially twice the velocity of said input means.
 4. The printer as claimed in claim 1 in which the characters on said first and second drums are arranged in lines with the lines of characters of said first drum being staggered with respect to the characters on the second drum when the drums are at rest, but the lines of characters of both said drums become aligned with a printing line during the dwells of their respective drums when oscillating at said resonant frequency; said lines of characters being parallel to one another and to the rotating axis of said shaft.
 5. The printer as claimed in claim 1 in which said first and second drums have equal rotating masses, and each of said drums has an inner end and an outer end, with the first drum having its outer end secured to said first area and the second drum having its outer end secured to said second area; the inner ends of said drums being adjacent to and spaced from each other.
 6. The printer as claimed in claim 2 in which said third connection area on said torsion shaft is midway between said first and second connection areas and in which said drums have rotating axes which are coincident with the rotating axis of said shaft.
 7. The printer as claimed in claim 2 further comprising first, second, and third groups of print hammers positioned along a print line and associated with said first, second, and third printer drums, respectively; each of the hammers of said groups of hammers being adapted to be energized when the associated one of said drums is experiencing a dwell.
 8. The printer as claimed in claim 7 in which the characters on said first, second, and third drums are arranged in lines which are parallel to the said rotating axis of said shaft; said lines of characters on said first and second drums being aligned with each other but offset with respect to the lines of characters on said third drum.
 9. The printer as claimed in claim 13 further comprising first and second groups of print hammers positioned along said print line and associated with said first and second printer drums, respectively; each of the print hammers of said groups of hammers being adapted to be energized when the associated one of said drums is experiencing a dwell.
 10. The printer as claimed in claim 3 in which said rotating means further comprises: a driving shaft detachably connected to one end of said input shaft; and support means for detachably and rotatably supporting the remaining end of said input shaft so as to enable said input shaft along with said torsion shaft, and said first drum and second drum secured thereto to be removed as a unit from said printer.
 11. The printer as claimed in claim 2 in which said first and second exciters are adjusted to operate in phase with each other.
 12. The printer as claimed in claim 11 in which the second drum has a rotating mass which is equal to the combined rotating mass of said first and third drums.
 13. The printer as claimed in claim 3 in which the characters on said drums are arranged in lines, with the lines of characters on the first printer drum being staggered with respect to the lines on the second drum when the drums are at rest; but the lines of characters of both of said drums become aligned wIth a printing line during the dwells of their respective drums.
 14. The printer as claimed in claim 3 in which each said exciter has radially aligned stator poles and rotor poles lying in planes which are parallel to and spaced from each other and which planes are perpendicular to the rotating axes of said first and second drums; said poles being trapezoidally shaped in cross section, with the rotor poles being attached to the torsion shaft for rotation therewith and the stator poles being stationary relative thereto.
 15. A printer comprising: rotatable input means including a torsion shaft having a plurality of connection areas thereon; rotating means for rotating said input means at a substantially constant velocity; first and second groups of printer drums, with each said drum being secured to said torsion shaft at one of said connection areas; and magnetically operated exciter means acting on the opposed ends of said torsion shaft to retard them as the torsion shaft is rotated by said rotating means to oscillate said first and second groups of drums at substantially the resonant frequency of said input means and drums to cause each group of drums to periodically dwell a predetermined number of times for each revolution of said input means; the drums of the first group experiencing said dwells at times when the drums of the second group are rotating at substantially twice the velocity of said rotating means; said exciter means including a first exciter located near one of said opposed ends of said torsion shaft and a second exciter located near the remaining said end; and said rotating means including a shaft of predetermined flexibility being connected to one end of said torsion shaft.
 16. The printer as claimed in claim 15 further comprising first and second groups of print hammers associated with the first and second groups of drums respectively; the first and second groups of print hammers being selectively actuated to effect printing when the drums of their associated groups are experiencing one of said dwells.
 17. The printer as claimed in claim 16 in which said drums have lines of characters thereon, with the lines being parallel to the rotating axis of said drums; and with the lines of characters of the drums of the first group being staggered with respect to the lines of characters of the drums of the second group.
 18. The printer as claimed in claim 1 in which said rotating means further includes an extension shaft on the remaining end of the torsion shaft, which extension shaft is identical to said input shaft; reaction masses secured to the free ends of said input and extension shafts; each said reaction mass having a supporting member to rotatably support the torsion shaft; and means for rotating the reaction mass secured to the input shaft at a constant velocity.
 19. The printer as claimed in claim 18 in which each supporting member is a tubular extension of its associated reaction mass, with each said tubular extension extending towards the associated said first and second connection areas and providing a bearing surface for rotatably supporting the torsion shaft.
 20. The printer as claimed in claim 19 in which the characters on said drums are arranged in lines, with the lines of characters of the first drum being staggered with respect to the lines of characters of the second drum while the drums are at rest, but the lines of characters of both said drums become aligned with a printing line during the dwells of their respective drums.
 21. The printer as claimed in claim 20 in which each said exciter has radially aligned stator poles and rotor poles lying in planes which are parallel to each other and perpendicular to the rotating axis of the torsion shaft. 